Batch cycle-001. Model 0.1.0, graph 0.2.0, parameters 0.1.0. 100 simulations, seeds 1 to 100; probes on 20. Every figure is a distribution over simulations of a structural model with seed parameter values; it shows what the model implies under these settings, not what will happen. Other nations are frozen at their 2026 ratings. No reconstructed historical data is used in this experiment.
Headline
United Kingdom played 20 rounds from 2026 under the mirror a peer method, with stochastic events, 100 times. Its capability index moved from 16.45 to a median of 17.33 (+0.87), with 90 per cent of simulations between 16.70 and 17.85 [experiment_objectives].
Starting position
In 2026 the nation ranks 3 on the index against the frozen field, holds 2 of nine domains at Tier 1 and has a tier rank of 5. Its base income is 951 credits a year, calibrated so that its 2026 position is affordable with headroom for investment.
What was decided
A simulation spent a median of 2,370 credits on moves. The five groups that took most were Nuclear Deterrence (partner, 188 credits, 7.5 per cent); Space Technologies (partner, 145 credits, 5.9 per cent); Semiconductors & Advanced Computing (buy, 132 credits, 5.4 per cent); Strategic Strike & Missile Defence (buy, 107 credits, 4.3 per cent); Resource Infrastructure (buy, 102 credits, 4.1 per cent) [experiment_decisions_by_group]. By mode: buy 50 per cent, partner 29 per cent, build 21 per cent [experiment_decisions_by_group]. Concentration of spending (HHI) had a median of 0.035, and the most repeated action appeared in 20 per cent of rounds.
The leading domain by period: rounds 1 to 5, National Security; rounds 6 to 10, National Security; rounds 11 to 15, Strategic Infrastructure; rounds 16 to 20, National Security [experiment_spend_by_period].
The method's chosen action was within 5 per cent of its best alternative in 78 per cent of moves and ahead by more than 25 per cent in 0 per cent [experiment_decision_margins].
What the world did
A median simulation saw 2 shocks and 1 upside events. The most damaging per firing were S01 (26 firings in 22 simulations, −23.9 points each); S08 (33 firings in 29 simulations, −23.8 points each); S09 (9 firings in 9 simulations, −23.1 points each) [experiment_shocks]. Upside events fired 143 times across all simulations [experiment_shocks].
The groups that lost most to shocks, per simulation: Fiscal Capacity & Public Finance −1.02; Economic Leverage & Dependence −0.99; Trade Facilitation & Logistics −0.92; Digital & Services Trade −0.89 [experiment_shock_damage_by_group].
The edges that carried most change through the graph, per simulation: Space Technologies to Space Operations (+0.68 points); Semiconductors & Advanced Computing to Artificial Intelligence (+0.62 points); Force Generation & Mobilisation to Land Power (+0.54 points) [experiment_propagation_by_edge].
Where it ended
At 2046 the median rank is 2 (5th to 95th percentile 2 to 2), the median count of Tier 1 domains 2 (0 to 6) and the median tier rank 5; the resilient score, the mean score sum over simulations, is 1,268 [experiment_objectives].
Tier 1 probability changed most in: financial strength (0 to 35 per cent of simulations); governance and integrity (100 to 76 per cent of simulations); human capital (0 to 37 per cent of simulations); production and innovation (100 to 56 per cent of simulations); strategic infrastructure (0 to 13 per cent of simulations) [experiment_tiers_by_round].
Why
Without shocks the index ends +0.349 higher on average, so the shocks cost about 0.349 index points [experiment_probe_attribution].
Holding instead of following this method changes the index by −1.326: that is the method's worth against doing nothing [experiment_probe_attribution].
Removing any single one of the five largest actions changes the index by between −0.012 and −0.001, for example 2039 partner Economic Leverage & Dependence (50 credits) [experiment_probe_attribution]. The largest actions by credits come late, when income is highest, and are rarely the most valuable.
Removing the largest shock of a simulation raises the index by +0.185 on average [experiment_probe_attribution].
The replay probe reproduces the simulations exactly (index change 0.000000), so the attributions are clean [experiment_probe_attribution].
Surprises
move_without_shock (warn): largest one-year move in a group with no shock landing: 3.33 points; 55% of simulations have one above 3.
tier_jump (warn): largest gain in one domain within five years: 4 tiers (8 simulations above 2).
retired_words (warn): e3-gbr-mirror-peer/report.md: 'simulations' 2 time(s), first near line 40; use 'simulations'.
The simulation furthest from the median (seed 33) ends −0.91 from it, with 7 shocks and 0 upside events [experiment_outlier_simulations].
Comparison
Against the hold experiment for the same nation (e3-gbr-hold), the median index is +1.19 points apart, the median rank 2 against 5, and Tier 1 domains 2 against 1 [experiment_against_hold].
No backcast comparison: this experiment does not start from a historical position [experiment_against_history].